Search techniques in which a search is performed by entering a search keyword in trying to find documents of interest from among vast document DBs accumulated on the Internet, an intranet, or a file server are powerful means that are often employed. Internet searches are often performed to gather past findings and related information regarding a certain theme for which no particular documents of interest are determined in advance. Thus, the user guesses search keywords that might return a document that s/he desires, and repeatedly performs searches while arranging ways of entering them to find useful information. On the other hand, with searches on intranets, file servers, or within client PCs, the existence of the target document is often known in advance, and the user executes searches by giving keywords for finding it. For example, if one wishes to refer to a proposal document that was sent to Corporation A a year ago, a search is performed giving “Corporation A,” content of proposal, sender of the document, etc., as keywords.
Today, document searches in corporate servers are often performed in corporations' handling of audits. In such cases, personnel outside of the department that is subject to audit, such as auditors, in-house audit departments, etc., or internal personnel, who have been instructed or indicated by such external personnel, execute searches for a relevant document. In other words, the person actually executing the search is often not the creator of the relevant document, and would therefore not immediately know what kind of documents are located where on file servers. Further, if there are a plurality of relevant documents, given the nature of audits, it would be required that they be found without any omission.
Incidentally, in common search systems, it is possible to enter one search keyword or a plurality of search keywords, and to include logical operations such as documents containing all such keywords (a logical product or AND search), containing any of them (a logical sum or OR search), containing none of them (a negative or NOT search), etc. As a result, it is possible to bring it closer to the target document group that the user is hoping for. In addition, many search systems support advanced searches based on combinations of logical operations, e.g., containing keywords C and either A or B. Further, with respect to displaying a list of search results returned, there are also search systems which display, in addition to file names (or web page titles) and in two to three lines, text that includes what precedes and follows the search keyword.
However, several problems arise when actually retrieving related documents using such search techniques. For example, assuming that an auditor is trying to retrieve budget documents, a case is considered where a search is performed specifying the keyword “budget” on a search system. Here, if the keyword “budget” is not used in the document(s) that the auditor wishes to refer to, and such words as “budg./act. figures,” or “business plan” are used therein instead, it/they will not be returned by the search. In other words, should one fail, at the time of the search, to come up with such synonyms for “budget” or words that encompass the concept of “budget,” some information will be missed. On the other hand, assuming that one did think of the keywords “budg./act. figures” and “business plan” and broadened the scope of search targets so as to contain any of “budget,” “budg./act. figures” and “business plan,” if thousands or tens of thousands of search results are presented as a result, there may be included many documents that are of no interest to the user, and it would be unrealistic for him/her to go through all of them. There is also a possibility that a document that the auditor wishes to refer to does not use any of the keywords “budget,” “budg./act. figures” and “business plan.” In other words, even with respect to the retrieval of related documents with no (or little) omission, if too many documents are returned in a search, it would be realistic to keep it down to a reasonable number by narrowing the search to some extent. Conversely, if no or too few documents are returned in a search, it would be necessary to broaden search possibilities by suggesting keywords that may be associated with the search keywords that the user entered.
Various techniques and methods have hitherto been studied with regard to such methods of selecting search keywords that would result in a reasonable search hit count largely including contents of interest. In Patent Document 1, for example, in order to have more contents of interest be included, conventional problems of not being able to search when keywords, while having the same meaning, are distinct, as in “climate” and “weather,” are overcome by assigning attributes to search keywords. In addition, in Patent Document 2, there is provided a means that refers to a thesaurus relating to a search keyword entered by the operator, takes into consideration the object of and a broader concept or narrower concept of the keyword, and automatically generates a query that the operator had implicitly intended. With respect to the generation of a query that would result in a reasonable hit count, Patent Document 3 and Patent Document 4 propose schemes that repeat the addition, deletion, expansion through synonyms, etc., of search keywords, thereby successively displaying the hit count obtained by the respective queries. These schemes display not only the query, but also how many hits there were in the search results for each of the search keywords contained in the query. In addition, Patent Document 5 proposes a scheme in which, when a document for which related documents are to be searched for is selected, a query that would result in a hit count closest to a pre-defined reference hit number is automatically generated while being dynamically altered.    Patent Document 1: JP Patent Publication (Kokai) No. 6-187374 A (1994)    Patent Document 2: JP Patent Publication (Kokai) No. 5-250411 A (1993)    Patent Document 3: JP Patent Publication (Kokai) No. 5-314182 A (1993)    Patent Document 4: JP Patent Publication (Kokai) No. 11-15841 A (1999)    Patent Document 5: JP Patent Publication (Kokai) No. 2005-100136 A    Patent Document 6: JP Patent Publication (Kokai) No. 2006-12078 A